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Description  |
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FIELD OF THE INVENTION
This invention relates to combined optical and electronic apparatus for
various types of image enhancement and more particularly to a system which
produces two images of the same scene which differ by a predetermined
property, and electronically subtracts the images to yield a video
difference signal which emphasizes or deemphasizes a predetermined
characteristic of the scene at which the apparatus is pointed.
BACKGROUND OF THE INVENTION
It has long been known that by suitable photographic processing involving
the use of positive and negative forms of an image that certain
characteristics of the image can be emphasized or deemphasized by the
overlay of various positive and negative images with suitable
translational or rotational displacements, density differences and/or
spacings. It will be appreciated, however, that processing and display
when utilizing strict photographic techniques is time consuming in view of
the length of time necessary to develop, prepare and position the positive
and negative images. This technique is thus not a real time technique and
thus is not applicable to on board target tracking systems in missiles,
guided projectiles and various other guided ordinances. Image enhancement
has also been accomplished in the past by use of Fourier Transformation of
a segmented image with appropriate transform manipulations enhancing or
deemphasizing a particular characteristic. This is usually accomplished
with a large amount of computer storage and the necessity of storing the
value of each point in a given image so that the appropriate Fourier
Transform manipulations can be performed. Thus in image enhancement by
computer processing, substantially all values in the input image must be
utilized in calculating each point in the output image and these values
must be stored and appropriately addressed so that the appropriate
transform can be applied. With the advent of the Fast Fourier Transform
(FFT), computer time has been significantly reduced. However, even with
the Fast Fourier Transform algorithm all points in the image must still be
sampled and stored, at least once, which still takes considerable time.
This technique is likewise not readily adapted to on board target tracking
systems. This is because the FFT processing results in a non-real time
system for image enhancement in which the final result may take as short a
time as 5 minutes for a 500 line TV picture or as long a time as several
days depending on the complexity and degree of enhancement required. Note
that a 500 .times. 500 line TV picture involves 250,000 elements. A 10,000
.times. 10,000 line picture typical of photographic resolution, requires
processing of 10.sup.8 elements.
Holography has also been used with spatial filtering for image enhancement
as a hologram involves Fourier Transforms, without need for computation.
However, the required photographic development and reprojections prevent
these techniques from being applicable to the above mentioned on board
apparatus. Also coherent illumination is necessary.
The subject system is a "real time" system which may be utilized on board a
guided missile, etc. The system involves two optical channels and a
point-by-point subtraction of the two images produced by the two channels.
This provides a video difference signal which represents the difference
between a positive and negative image of the scene at which the system is
pointed. In terms of Fourier Transforms, the transform of the image equals
the transform of the object multiplied by the transfer function of the
optical system.
In this patent a number of techniques are enumerated that allow synthesis
of a wide variety of transfer functions which lead in turn to a variety of
spatial filter effects on images. Translational, rotational, density
and/or magnification differences between the two images can be optically
or electronically introduced to provide, for instance, edge enhancement,
size discrimination, enhancement of a particular set of parallel image
lines, and peripheral image enhancement or enhancement of the center of
the image, sometimes called "boresite" enhancement. It should be noted
that while some of the above enhancements may be accomplished by Fourier
Transform manipulations, in a computer or holographic manipulations,
different effects depending on location of the image plane are not
achieveable by such techniques. These enhancements are those which are a
function of position in the image plane. Thus, in addition to the real
time aspect of this invention, there is the added capability of providing
non-Fourier Transform enhancements.
In essence, the subject system provides the equivalent of two optical
systems referred to herein as "two barrel optics" in which the receptors
of these two optical systems are scanned point-by-point in a twin scan
system with the outputs from the scanning apparatus being subtracted on a
real time basis, and with the video difference signal then being displayed
on a conventional raster scan device. The desired enhancement, or
deemphasis, is obtained by controlling the image difference parameter
between the images in the optical channels such that the positive and
negative images are electronically superimposed in a manner similar to the
photographic process.
In one embodiment the subject system is designed for edge enhancement and
size discrimination so that an image may be enhanced over background
clutter by virtue of its sharp edges as well as its small size as compared
to background objects. This may be important in, for instance, picking an
aircraft out of clutter involving clouds behind the aircraft. In this case
it will be appreciated that the aircraft is much smaller than the clouds.
Moreover the aircraft has sharp edges as opposed to the usual cloud
configuration in which the edges of the clouds are not as sharply defined.
In one embodiment this is accomplished by utilizing a "two barrel" system
and by scanning the images produced, with the image produced by one barrel
being blurred by receptor offset from the focal plane of this barrel. This
is called the "focus-defocus" case. For the present purposes the term "two
barrels" refers to two optical systems or channels in which each barrel
produces an image. This system involves a "parallel twin scan" in which
two parallel moving scanning beams are produced, one scanning one image
and the other scanning the other image. The scanning beams simultaneously
read out a corresponding element or corresponding location on each of the
receptors. As will be discussed later, the same result can be achieved in
a one barrel system with appropriately weighted summing or averaging of
elements adjacent to the scanned element providing a simulated blurr.
Emphasis of a particular series of parallel lines, with simultaneous
deemphasis of orthogonally oriented lines, may be accomplished by a twin
scan two barrel system, with one scanning beam being offset with respect
to the second scanning beam in a direction orthogonal to the line to be
emphasized. This means that while one beam scans a given element in one
image the other beam scans an adjacent element in the other image. The
deemphasized lines will be the lines in the direction of the scan offset.
This same line emphasis/deemphasis can also be accomplished with parallel
twin scan and a skewing of the optical axes in the two barrel system with
the offset angle in the direction of the deemphasized lines. The skewing
displaces the position of one image with respect to the other image to
yield the same result as the offsetting of one scanning beam.
The subject system also permits peripheral image enhancement in which
circumferential line elements of objects at the periphery of the image
plane are enhanced over those at the center. This is accomplished in one
embodiment in a two barrel system with a parallel twin scan arrangement,
with the two optical systems having slightly different magnifications. In
another embodiment radial line peripheral enhancement utilizes a two
barrel system with rotationally displaced receptors and a rotationally
displaced twin scan system with the rotational offset providing the radial
line peripheral enhancement.
Another type of peripheral image enhancement involving line symmetry
enhancement at the periphery of the image may be accomplished by a
parallel twin scan system with identical optical channels, in which the
two barrels have parallel optical axes but the receptors are skewed about
the line of intersection of their superimposed receptor planes.
Additionally, orientation independent peripheral image enhancement may be
accomplished with the use of a two barrel, parallel twin scan system and
field flattening optics at the image plane of one of the barrels, with
focal plane coincidence of the two optical systems at the center of the
overlapped images.
Central image or boresite enhancement, on the other hand, can be
accomplished with parallel twin scan apparatus and a field flattening
optics at the image plane of one of the two barrels, with focal plane
coincidence of the two optical systems at the outer edge of the overlapped
images. The same type of central image or boresite enhancement may also be
accomplished by use of a centrally weighted, radially-weakening density
filter at the image plane of one of the optical systems.
In general the above systems can be characterized as follows:
visual image displayed = .sup.-.sup.1 { f(a.sub.x, y) -f(b.sub.x, y)} ,
where f is a monotonic function,
where a.sub.x, y is the voltage on an image point in the (a) channel at
coordinates (x, y),
where b.sub.x, y is the voltage on an image point in the (b) channel at
coordinates (x, y),
In general:
a(x, y) = .intg.l(x', y') G.sub.a (x-x', y-y') dx'dy'
where G (x-x', y-y') is the point spread function of a point imaged at
coordinates (x', y'); as seen at image coordinates (x, y)
where image coordinates (x, y) = M.xi., M.eta.); where M is magnification;
and where .xi., .eta. are the orthogonal coordinates of the object in the
object plane; and where l(x', y') is the "idealized" image intensity
corresponding to the object intensity at (M.xi.', M.eta.'),
The point spread function is the variable in terms of apodization in the
lens plane, lens system characteristics or receptor orientation and
location in the (a) channel.
b.sub.x, y =.intg.l(x', y') G.sub.b (x-x', y-y') dx'dy'
Possible monotonic functions, f, applied as above, may result in images
related to the original such as
##EQU1##
among others, and since all of these are nonlinear, they may yield types
of enhancement that cannot be performed by Fourier Transforms.
It will be appreciated that in all the above enhancement techniques the
twin scan outputs are differentially added to give the aforementioned
video difference signal which is then presented by a conventional raster
scan display. Ratios of twin scan output signals and other functions also
provide for a variety of image enhancement possibilities not coverable
with Fourier Transform methods and are included as part of the subject
invention.
What has heretofore been described involves analog processing by virtue of
certain optical arrangements to provide for various types of image
enhancement/deemphasis via electronic positive and negative image overlay.
However, similar results can be obtained with some time lag by the use of
digital processing with a single barrel system through the use of digital
processing to simulate translational offset, rotational offset and various
adjacent element weighted summing or averaging heretofore mentioned.
The enhanced image, as described above, can always be added to unprocessed
positive (or negative) image, with mixtures of the original and enhanced
images in any proportion. Aside from what aids such mixtures may provide
to an observer, such mixtures can be used for equalization of spatial
frequencies analogous to audio equalization in hi fi equipment. For
example, if the modulation transfer function of an imaging system trails
off with increasing spatial frequency (as it always does), and if
signal/noise is sufficiently good, much of the roll - off can be
compensated by adding an amplified version of focus-defocus enhancement
(essentially with a S.sup.2 low-end roll-off) to the original image, which
tends to equalize the optical qualities up to the high end roll-off of the
enhanced image.
A further possibility is to combine the original unenhanced image, in black
and white, (on a color display) with the enhancement signal, derived as in
the above description, converted to a chroma parameter. There are several
ways to do this, as the chroma signal provides two degrees of freedom. One
way is to: choose the hue, say red, as fixed. Let the overlay signal
control saturation (while unenhanced picture controls gray level). Choose
the degree of saturation, and let the overlay control hue. Then pick an
1:1 relationship between hue and saturation or between Q&I signals. Then
define a path in chroma space and let the overlay control position along
this path. The "spare" degree of freedom, at least in principle, permits
two independent overlays. For example, using displacement between imagers,
and three devices, one can obtain: 1. a straight picture, 2. a left-right
displacement, 3. up-down displacement. Now, let the straight picture
operate the black and white channel; let the left-right displacement
operate the I signal, and let the up-down displacement operate the Q
signal. Thus we have two independent overlays presented simultaneously on
one screen.
In another embodiment, in a two barrel system, using separate lenses it is
possible to have different size and shape aperture stops in each one, e.g.
a square aperture in one and a circular aperture in the other. This will
tend to emphasize certain shapes of objects, in this example objects with
fourfold symmetry and the right orientation. The differences could be even
more subtle, e.g. different apodizations in the aperture planes of the two
lenses. The apodizations may simply have radial variation about the lens
axis; more generally they may have circumferential variation, which would
tend to emphasize objects of certain shapes of symmetries as well as
sizes.
Aperture stops of apodizing filters can be applied sequentially, in
alternation with a single lensing system as well as simultaneously in two
lensing systems, if picture motion is not too rapid.
It will be appreciated that a computer or electronically controlled
apodizing screen may be utilized in the aperture plane (which can itself
be a video image or pattern, say on a liquid crystal display, or on a
schlieren medium such as the oil film in a G.E. light valve, where an
electron beam "writes" a schlieren pattern on a surface, to be in a lens
plane for this application. Rapidly changing and controlled apertures can
be formed ahead of one or the other optical channels. In other words, with
a 2-D imaging screen capability in the lens plane, different for each
lens, one can either "write in" specifications corresponding to the
desired emphasis characteristics or, "closing the loop", "lock on" to an
acquired image.
It is therefore an object of this invention to provide a real time optical
processing system for image enhancement involving the generation of a
video difference signal from scanning the images developed by two optical
channels, either actual or simulated.
It is another object of this invention to provide improved apparatus for a
wide variety of image enhancement/deemphasis results in which edge
enhancement, size discrimination, plane emphasis/deemphasis, peripheral
image enhancement and/or central image or boresite enhancement is
provided.
It is another object of this invention to provide novel image enhancement
apparatus and methods involving real time processing and point-by-point
treatment of images in which only a pair of image values are necessary at
any given period of time for the generation of an enhanced image.
These and other objects of this invention will be better understood in
connection with the following description in view of the appended drawings
in which:
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagramatic representation of one embodiment of the subject
invention in which edge enhancement and size discrimination are
accomplished by virtue of the generation of a video difference signal;
FIG. 2 is an illustration of a typical scene for which image enhancement is
desired;
FIGS. 3A and 3B illustrate diagramatically the display of the scene of FIG.
2 prior to and after edge enhancement and size discrimination afforded by
the apparatus of FIG. 1;
FIG. 4 is a diagramatic representation of the point spread function of an
object projected onto an image plane;
FIG. 5 is a diagramatic representation of a two barrel system in which an
object on an object plane is focused by the two barrel system to a single
image plane, also indicating the point spread functions of the focused
image of one barrel and a defocused image of the other barrel with the
difference function illustrating negative as well as positive going
components of the point spread function of the difference.
FIG. 6 is a diagramatic and schematic representation of a single barrel
system for edge enhancement and size discrimination utilizing a single
scan with simultaneous readout of elements adjacent the scanned element;
FIG. 7 is a diagramatic representation of the generation of the simulated
blur image by virtue of reading out adjacent elements to a scanned
element;
FIGS. 8A and 8B are diagramatic illustration of orientation discrimination
by virtue of translation or offset in a twin scan process in which one of
the scanning beams is offset in a predetermined direction to deemphasize
elements of an image in this direction, while emphasizing elements
perpendicular to the offset;
FIG. 9 is a diagramatic illustration of a system for orientation
discrimination by virtue of translation engendered by the skewing of the
optical axis of one of the optical systems with respect to the optical
axis of the other of the optical systems in a parallel twin scan
embodiment;
FIGS. 10A and 10B represent a circumferential line peripheral image
enhancement system in which optical systems of different magnification are
utilized to produce peripheral enhancement;
FIGS. 11A-11C represent a radial line peripheral enhancement system to
produce peripheral enhancement;
FIGS. 12A and 12B illustrate a system for line symmetry peripheral image
enhancement in a parallel twin scan system in which identical optical
systems are utilized with skewed receptor planes to produce line symmetry
peripheral image enhancement;
FIGS. 13A and 13B illustrate a central or boresite image enhancement system
utilizing a field flattening element in one of the optical channels to
produce central image enhancement;
FIGS. 14A and 14B are diagramatic illustrations of the image surface
coincidence at the periphery of an overlay image, for boresite
enhancement;
FIGS. 15A and 15B are diagramatic illustrations of image surface
coincidence at the center of an overlay image for orientation independent
peripheral image enhancement;
FIGS. 16A through 16E illustrate a central/peripheral image enhancement
system with focus-defocus enhancement and size discrimination utilizing
parallel twin scan with alternatively a centrally weighted, radially
weakening density filter or a peripherally weighted radially weakening
density filter offset from the image plane of one of the optical sytems
for opposite type enhancements;
FIGS. 17A-D illustrate one form of apodization as a method for introducing
selected image enhancements;
FIG. 18 is a generalized diagram enumerating the types of enhancement
available with the subject invention; and
FIG. 19 illustrates a digital approach and a single barrel system for
producing a variety of different image enhancements.
DETAILED DESCRIPTION
Referring now to FIG. 1 in one embodiment arranged for edge enhancement and
size discrimination the subject invention includes a two barrel imaging
system diagramatically illustrated by optical elements 10 and 12. These
optical elements are focused at infinity and are arranged with parallel
axes 14 and 16. An image 18, illustrated as a point on an object plane 20
is focused by optical elements 10 and 12 to a single focal plane 22. In
this embodiment the optical systems represented by optical elements 10 and
12 are identical. For purposes of discussion the image produced by optical
element 10 will be said to be formed in a first optical channel while the
image formed by optical element 12 will be said to be formed in a second
optical channel.
With respect to the first optical channel, an image receptor 24, which may
be of any of a wide variety of image receptors, is located in focal plane
22. Locations on the receptor are labelled i and j which designates a
location in orthogonal coordinates with the origin of the coordinates
being axis 14, the optical axis of the first channel. "a.sub.ij " is the
signal due to the image associated with this location or address.
The image receptor for the second channel is indicated by reference
character 26 and is offset from the focal plane by a focus offset 28.
Receptor 26 therefore lies in a plane parallel to the focal plane and is
offset by a given distance. Images on receptor 26 are indicated by
b.sub.ij where the ij location is in orthogonal coordinates, with the
origin of the orthogonal system being axis 16, the optical axis of the
second channel. The locations are designated such that the distances
measured from each of the origins are in the same units. Thus, an image
a.sub.ij in the first channel corresponds to an image b.sub.ij in the
second channel for objects sufficiently far away from the subject
apparatus (e.g. parallax is minimal). The receptors for each channel are
read out in one embodiment by conventional scanning devices 30 and 32 in a
twin scan mode which refers to the simultaneous readout of the receptors
in each channel at corresponding points or locations. Thus, in this
embodiment, an image a.sub.ij is read out simultaneously with an image
b.sub.ij. This can also be accomplished by controlled read out of a matrix
type receptor such as a charge coupled matrix with individual matrix
elements.
Thus it will be appreciated that the readout and scanning system may
include conventional image orthocons wherein the intensity of the image at
the receptor is read out as a signal having an amplitude proportional to
the intensity of the image. Alternatively, the image receptor may be a
charge coupled device (CCD) which is read out by XY addressable drive
units which may be made to scan the respective CCD device. It will be
further appreciated that when corresponding locations on the receptors are
read out this corresponds to a parallel twin scan as distinguished from
twin scan in which corresponding pairs or points are read out where the
points are not at the same location relative to the origin. In this latter
embodiment certain translational abberations can be introduced to
emphasize various planes by simultaneously scanning adjacent points as
will be described in connection with FIGS. 8A and 8B.
In all the systems to be described, the outputs of the scanning units are
differentially added by differential amplifier 34 such that the output of
the differential amplifier is a video difference signal which is coupled
to a suitable video display 36 which is scanned in a manner commensurate
with the scanning of the image receptors. This display can be a
conventional CRT display or an XY addressable matrix in which a raster
scan type drive system is utilized. In general, receptor and display may
also be scanned in non-raster forms, as long as both are synchronized.
Because image receptor 26 is offset from the focal plane, the image at the
receptor, herein referred to by reference character 40, is blurred. That
is to say the image blur size with respect to an image at 42 at the focal
plane on image receptor 24 is larger than for image 42 by a predetermined
amount. When the scanning apparatus scans the image receptors and the
result is displayed, the image displayed emphasizes the sharp edges of the
image while washing out dull edges and gradual shading. It is assumed that
video gains are adjusted to take maximum advantage of the enhanced image,
whose contrast is generally reduced by the subtraction process unless the
gain is suitably increased. Moreover, all objects on the object plane will
appear to be washed out if their size exceeds the size of the blur 40
projected back to the object plane. Thus the resolution of the system as
indicated by arrow 44 relates to the blur size as indicated by arrows 46
which is in turn determined by the focus offset 28.
This is useful in resolving small objects with respect to backgrounds which
are large in extent. This situation can be better understood with
reference to FIG. 2.
Referring now to FIG. 2 is a scene suitable for enhancement may include an
aircraft 50 which is in front of cloud cover generally indicated at 52.
The aircraft is located above a horizon 54, the importance of which will
become apparent hereinafter. As illustrated in FIG. 3A an unenhanced
portion of the scene in FIG. 2 may include the aircraft 50 in front of
background clutter comprising clouds 52. However, by virtue of the system
described in connection with FIG. 1, that which will be displayed on the
display 36 of FIG. 1 is the outline of aircraft 50 in which the edges of
the aircraft are that which are visible. The system of FIG. 1 has
therefore not only discriminated against gradually changing portions of
the scene such as the clouds which in general do not have sharp defined
edges, but also has washed out objects larger than the aircraft with the
appropriate setting of the blur size and focus offset to resolve objects
having a length equivalent to aircraft and to discriminate against all
other objects which are larger. In systems to be described in connection
with FIGS. 8A and 8B and FIG. 9 it is possible to wash out the horizon
line such that when aircraft 50 is near the horizon it can be emphasized
with deemphasis of the horizon. In the FIG. 1 embodiment it will be
appreciated that nothing here is absolutely washed out, but edges of
aircraft are least affected, while clouds and other low spatial frequency
objects are most affected. The horizon comes out inbetween.
The theoretical underpinings of the operation of the system of FIG. 1 are
now described in connection with FIGS. 4 and 5. This explanation will also
aid in the understanding of the different types of image enhancement and
deemphasis described in connection with other embodiments of the subject
invention.
Referring now to FIG. 4 the concept of a point spread function for an
optical system will be developed. In this diagram an object 60 in an
object plane 62 is focused by a lens system 64 onto an image plane 66. The
intensity is a function of position and is given by the point spread
function 68 which is the intensity of light along the image plane. As can
be seen a point source of light at 60 produces not only light at the image
point but also, depending on the quality of the optics, more or less light
at points removed from the image point. By theorems well known in optics,
any image is a convolution of the idealized image with the point spread
function which would be a unit impulse (or a Dirac delta function) if the
lens were "mathematically ideal." In actual physical systems there is
always a blur circle of finite size, resulting from a combination of
diffraction effects and geometric aberrations. The worst of these
generally dominates any specific case, and the other may be ignored in
practice.
Referring to FIG. 5, to the system of FIG. 4 is added a second identical
optical system with a lens 70 arranged so that its focal plane is
coincident with the focal plane of lens 64. In this system a blurred out
image is formed at another plane 72 removed from the image plane of lens
70, and a first order approximation of the point spread function is
illustrated to the right of this blurred out image. The offsetting of the
receptor in the second channel changes the point spread function in this
channel. When the point spread function at A is subtracted from the point
spread function at B as illustrated in FIG. 5 a composite point spread
function is formed in which the point spread function may go negative as
illustrated at points 74. Thus C represents a modified point spread
function. The result is that for a given image, high spatial frequencies
(edges) are emphasized and low spatial frequencies (no-edges, unbroken
extent, gradual intensity graduations) are deemphasized. The reason for
this is that an edge represents a step function yielding a spatial
frequency spectrum, proportional to 1/F, where F is spatial frequency. The
frequency spectrum in this case refers not to the wavelength of the light
utilized but rather refers to the change in intensity of the light with
respect to position in cycles/mm (for example). A high frequency
represents a very rapid change with position and a low frequency a gradual
change. By virtue of the subtraction of the blurred image from the focused
image which yields a transfer function F.sup.2 times that of the focused
system alone, rapid variations tend to be emphasized and gradual ones
suppressed. It will be appreciated that the smaller the blur spot or
circle the less will be the emphasis of the edges and the larger the blur
circle the more clutter rejection and the more edge and point or small
object emphasis. The reason for this is that the blur size in part
determines the frequency below which this F.sup.2 -proportional behavior
is dominant. As mentioned before the system also results in washout of all
objects on the object plane which are larger than the resolution size
which is defined by the projection of the blur circle back to the object
plane. Thus the subject system in addition to favoring high spatial
frequencies also has a resolution characteristic commensurate with the
blur circle size.
Referring now to FIG. 6, a single barrel system may be utilized to simulate
the two channels of the aforementioned embodiment and to simulate the
blur. In this case a single barrel system diagramatically illustrated at
FIG. 7, shows the matrix to include a number of elements 84 each having a
different orthogonal address, ij, from the center of the matrix. The blur
is simulated in this embodiment by the simultaneous readout of all the
elements within, for instance, a dotted box 86 which includes as a central
element the ij element which is at that moment of time being read out or
scanned. Referring back to FIG. 6 this can be accomplished electronically
as is conventional by a scanning device 88 which scans in sync with the
simultaneous read out system 90. The simultaneous read out system and the
scanning device are synchronized such that as the scanning device scans
the matrix, the adjacent elements to the scanned element are
simultaneously read out and summed as illustrated at 92. This may be a
weighted sum in one embodiment. By weighted sum is meant that terms
corresponding to different distances from the ij coordinates are
multiplied by different coefficients (+ or -) before the sum is taken.
This in essence integrates the intensity of the image over a number of
elements adjacent the element being scanned as is the case when a blur
circle is utilized. The direct output from the scanning unit is delayed by
a conventional delay unit 94 which compensates for the time required in
the summing process. This may be either infinitesimally small or, if
computers are utilized, the computation time must be taken into account.
The outputs of the weighted summing device and the delay device are
applied to a differential amplifier 96, the output of which is applied as
mentioned before to a conventional raster scan type display such that edge
enhancement and size discrimination are achieved in a single barrel
system.
It will be appreciated that the blur size can be altered by the programming
of the simultaneous read out unit so that any given number of elements
surrounding the scanned element can be simultaneously read out with an
increasing perimeter defining an increased blur size.
The previous discussion has centered around one type of enhancement, i.e.
orientation independent edge enhancement. As the name would suggest, this
enhancement is independent of the orientation of the image. It is
sometimes useful to be able to either emphasize or deemphasize edges or
structures which lie in a given set of directions or along a given set of
lines. As mentioned hereinbefore, it is oftentimes desireable to
deemphasize a horizon while emphasizing shapes above the horizon which are
not parallel to it. This is accomplished in a "double barrel" system
illustrated in FIG. 8A in which receptors for the two barrels lie in a
common image plane.
In this embodiment the two barrels are represented by lens systems 100 and
102 which are identical and are axially offset such that the central axis
or optical axes of the systems are parallel. Thus the systems share an
image plane 104 at which receptors 106 and 108 are respectively located.
This system also utilizes a twin scan system, with scanning units 110 and
112 scanning respective receptors and with their outputs differentially
summed at a differential amplifier 114.
This system is not however a parallel scan system but rather the scanning
location at receptor 108, herein labelled i+x, j, is offset or translated
by a predetermined amount from the co-scanned location ij at receptor 106
at any given instant of time. The x direction of scanning beam offset, if
in the horizontal direction results in a video difference signal at the
output of a differential amplifier 114 which deemphasizes horizontal lines
while emphasizing vertical lines when displayed. It will be apparent that
either by virtue of rotation of the complete apparatus or by appropriate
control of the scanning beams any particular line orientation can be
chosen as a deemphasized line with a line orthogonal thereto being
emphasized. The first situation is illustrated in FIG. 8B.
Referring to FIG. 9 the same result is achieved by skewing the axis of lens
system 102 such that a focused spot is displaced in the x direction. As
illustrated in this case, parallel twin scan apparatus may be utilized
such that scanning unit 120 and scanning unit 122 parallel scan receptors
106 and 108. Thus corresponding locations on each receptor are
simultaneously scanned as illustrated by the a.sub.ij /b.sub.ij notation.
The outputs when differentially added by differential amplifier 114 result
in the same type of plane emphasis/deemphasis as described in connection
with FIGS. 8A and 8B. It will be appreciated that the line orientations
deemphasized will be parallel to the direction of axis skew.
Another type of image enhancement is illustrated in FIGS. 10A and 10B and
FIGS. 11A - 11C. In these embodiments objects at the periphery of the
image are emphasized while the central image is relatively washed out.
This type of imaging system is important in the detection of objects just
entering the field of view. The system illustrated in FIG. 10A is a
two-barrel parallel twin scan system in which an object 130 on an object
plane 132 is focused by two different lens systems 134 and 136. The
characteristic of this system is the difference in magnification of the
lens systems. The difference in magnification causes emphasis of
circumferential lines at the periphery of the image. In this embodiment
there are two different image planes and corresponding receptors located
at these image planes. These receptors are indicated respectively at 138
and 140. The parallel twin scan is, as mentioned hereinbefore,
accomplished by synchronized scanning units, herein referred to as
scanning unit 142 and scanning unit 144, the outputs of which are coupled
to a differential amplifier 146 to provide the required difference signal.
The parallel scan is illustrated by the corresponding scan locations
a.sub.ij and b.sub.ij. The resulting circumferential peripheral image
enhancement is illustrated in FIG. 10B and occurs when the output of
differential amplifier 146 is applied to a conventional raster scan
display. In this figure the heavier density of circles indicates enhanced
intensity.
For radially lying images, peripheral enhancement may be achieved by
rotationally displaced image planes and such a system is illustrated in
FIGS. 11A through 11C. Referring to FIG. 11A an object 141 is focused via
identical lensing systems 143 onto rotationally displaced image receptors
A and B both located in focal plane 145 which is the same for both lensing
systems. The rotation of the receptors is illustrated in FIG. 11B. In this
embodiment, one receptor is rotated with respect to the other about what
is effectively the common origin of the receptors, such that corresponding
points on the receptors are in effect locally translated one from the
other by a magnitude proportional to distance from center, and in a
circumferential direction. Referring back to FIG. 11A, a rotationally
displaced twin scan system is diagramatically illustrated in which
scanning units 145 and 147 are operated in synchronism. The outputs from
these units are differentially added at 149 to produce a video difference
signal.
In this scanning arrangement each scanning unit scans a corresponding
element or location on its respective receptor. Since the receptors are
rotated with respect to each other, the scans correspondingly are rotated.
Thus the A receptor intensity at ij is read out simultaneously with the B
receptor intensity at the corresponding ij location. In this case
locations on a receptor are measured relative to the coordinates of the
receptor and any scanning system which reads out corresponding locations
simultaneously on each receptor is within the scope of this invention.
Since the receptors are rotated it will be apparent that at their
peripheries the local image translation will be maximized, whereas at the
center very little if any translation will occur. When the images at these
receptors are electronically subtracted, radial elements or lines will be
emphasized at the periphery of the reconstructed image as illustrated in
FIG. 11C, with the centrally located radially aligned images being more
and more washed out towards the center of the image.
Referring to FIGS. 12A and 12B, a system which enhances elements towards
that portion of the periphery of the image which is furthest from an image
intersection line can be achieved in a two barrel system with identical
lensing systems 150 and 152 with parallel axes and receptors in skewed
projection planes 154 and 156. Parallel twin scan is utilized with
scanning units 158 and 160 having outputs differentially summed at 162.
The result of the parallel twin scan is illustrated in FIG. 12B with
peripheral image enhancement illustrated as the denser shading, indicating
enhanced elements at that portion of the periphery of the image removed
from line 163. Line 163 represents the intersection of projection planes
154 and 156 when one is superimposed on the other. Obviously this line can
be given any desired direction and position so as to deemphasize objects
in a given band as illustrated by arrows 164. This is referred to as line
symmetry peripheral enhancement.
Referring now to FIGS. 13A and B and 16A, B and C, if it is desireable to
enhance the center portion of the image, the subject system may be
utilized in a double barrel approach as illustrated in FIG. 13A with
lensing systems 170 and 172 being of identical nature with parallel
optical axes. In this embodiment receptors 174 and 176 are located along
the image planes of these respective optical elements and a parallel twin
scan system is again used, with scanning units 178 and 180 having outputs
coupled to a differential amplifier 182. In this embodiment a conventional
field flattening element 184 is located at the receptor for one of the
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